Emergency medicine is the medical specialty concerned with the care of illnesses or injuries requiring immediate medical attention. Emergency physicians (often called “ER doctors” in the United States) specialize in providing care for unscheduled and undifferentiated patients of all ages. As first-line providers, in coordination with emergency medical services, they are primarily responsible for initiating resuscitation and stabilization and performing the initial investigations and interventions necessary to diagnose and treat illnesses or injuries in the acute phase.